improvements when plc is switched off

- stop continuous logging during reconnect
- include ._init() into lock

frappy_psi/logo.py

@@ -19,6 +19,8 @@
 #   Markus Zolliker <markus.zolliker@psi.ch>
 #
 # *****************************************************************************
+import sys
+import time
 from ast import literal_eval
 from threading import RLock
 import snap7
@@ -31,22 +33,45 @@ class IO(Communicator):
     tsap_server = Property('tcap_server', IntRange())
     ip_address = Property('numeric ip address', StringType())
     _plc = None
+    _last_try = 0
+
+    def initModule(self):
+        self._lock = RLock()
+        super().initModule()
 
     def _init(self):
         if not self._plc:
-            self._lock = RLock()
+            if time.time() < self._last_try + 10:
+                raise CommunicationFailedError('logo PLC not reachable')
             self._plc = snap7.logo.Logo()
-            self._plc.connect(self.ip_address, self.tcap_client, self.tsap_server)
-            if not self._plc.get_connected():
-                raise  CommunicationFailedError
+            prev_stderr = sys.stdout
+            sys.stderr = open('/dev/null', 'w')  # suppress output of snap7
+            try:
+                self._plc.connect(self.ip_address, self.tcap_client, self.tsap_server)
+                if self._plc.get_connected():
+                    return
+            except Exception:
+                pass
+            finally:
+                sys.stderr = prev_stderr
+            self._plc = None
+            self._last_try = time.time()
+            raise CommunicationFailedError('logo PLC not reachable')
 
     def communicate(self, cmd):
-        self._init()
         with self._lock:
+            self._init()
             cmd = cmd.split(maxsplit=1)
             if len(cmd) == 2:
                 self._plc.write(cmd[0], literal_eval(cmd[1]))
-            return self._plc.read(cmd[0])
+            try:
+                return self._plc.read(cmd[0])
+            except Exception as e:
+                if self._plc:
+                    self.log.exception('error in plc read')
+                self._plc = None
+                raise
+
 
 class Snap7Mixin(HasIO):
     ioclass = IO